The invention relates to an apparatus for manufacturing a fiber mass suspension, the apparatus comprising a pulper for mixing together a fiber material and water so as to produce a fiber mass suspension and for dividing the fiber mass suspension into an accept fraction and a reject fraction, the accept fraction being arranged to be forwarded to a further treatment process of the fiber mass suspension and the reject fraction being arranged to be supplied for further processing.
The invention further relates to a method of manufacturing a fiber mass suspension, the method comprising producing the fiber mass suspension by an apparatus which comprises a pulper, the method comprising producing the fiber mass suspension by mixing together a fiber material and water in the pulper, dividing the fiber mass suspension into an accept fraction and a reject fraction, forwarding the accept fraction to a further treatment process of the fiber mass suspension, and supplying the reject fraction for further processing.
At an initial stage of manufacturing a fiber mass suspension, such as a fiber mass suspension to be used for manufacturing paper and cardboard, pulpering may be used as one part of the process. The purpose of pulpering is to defiber a fiber material to be fed to a pulper provided in the pulpering system as well as to mix the fiber material with water to be fed to the pulper so as to produce a fiber mass suspension. The fiber material to be used may be e.g. cellulose or a recycled fiber material or a fiber-containing material from a paper or cardboard factory.
The accept, which is a portion that has passed through a screen plate provided at the bottom of the pulper, is supplied further in the fiber mass suspension manufacturing process. A portion of the fiber mass suspension that does not pass the screen plate, i.e. the reject, is further supplied to a secondary pulper by means of a reject removal pump. The secondary pulper continues processing the reject, dividing it into an accept part and a reject part. The reject formed in the secondary pulper is further supplied to a drum screen for the purpose of recovering from the reject received from the secondary pulper fibers still remaining therein for a fiber mass suspension manufacturing process. The remaining material, i.e. the reject formed at the drum screen, in turn, is removed from the process, to be burned outside the process, for instance.
Typically, such a process has to be used e.g. such that during a reject collecting phase the reject is allowed to flow from the pulper to the secondary pulper for a predetermined period of time, after which the reject flow from the pulper to the secondary pulper is prevented. Next starts a reject deflaking phase wherein a reject mass received from the pulper is processed for further screening and defibering. A material sufficiently defibered at the secondary pulper may be supplied as the accept of the secondary pulper back to the pulper. The next phase to start is reject washing wherein water is supplied to the secondary pulper to wash fiber material from the reject; the fiber material may be further supplied to the pulper. The reject that remained at the secondary pulper is supplied to the drum screen, wherefrom water and fiber are recovered to the process and the precipitated reject is supplied to reject processing. During reject processing, the flow of any new reject material from the pulper to the secondary pulper is thus prevented. According to another use, the flow of the reject material from the pulper to the secondary pulper is prevented for at least until the reject that remained at the secondary pulper has been fed to the drum screen. In both cases, the process thus has to be used as a kind of a load or batch process such that for most of the time the flow of the reject from the pulper to the secondary pulper is prevented. Consequently, the pulpering system requires two secondary pulpering systems in parallel in order to achieve a higher output.